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Eight-legged epicure

Do some spiders trap and feed on mosquitoes? Considering that the female mosquito, after feeding, would be a great source of protein, it would seem a good target. Or have mosquitoes evolved an evasive technique for spider webs?

Just as we humans have individual, sometimes unusual, tastes—such as liverwurst, Jell-O with shredded carrots, and stinky cheeses—our eight-legged friends have theirs. Although spiders mostly dine on whatever potential prey comes their way, some spiders find mosquitoes particularly pleasing to the palate.

One species, a jumping spider from East Africa, seems to have a special preference for female mosquitoes that have had a recent blood meal. In laboratory studies, the spiders consistently choose blood-fed mosquitoes over sugar-fed ones. In doing so, the spiders feed indirectly on blood from vertebrates. No spiders are known to feed directly on vertebrate blood because they lack the necessary specialized mouthparts.

When a female mosquito gorges on blood, her mass may increase more than 200 percent. The increase in mass makes the mosquito slower and less agile, and, therefore, an easier target for predators. East African jumping spiders do not pursue blood-fed mosquitoes simply because they learn that full mosquitoes are easier to catch. The preference is instinctive. Even captive spiders that had no prior experience with mosquitoes prefer the smell of blood-fed mosquitoes.

Juvenile East African jumping spiders prefer mosquitoes from the genus Anopheles, the type of mosquito that carries the parasite that causes malaria. Anopheles mosquitoes have a distinctive resting posture, with their hind legs raised and their abdomen angled upward at 45° to the surface on which they are standing. Other species rest parallel to the surface.

Anopheles mosquitoes' posture makes them vulnerable to attack by the young jumping spiders, which sneak up behind the mosquitoes, crawl under them, and grab them from beneath. The tactic allows a young spider to overpower a mosquito many times its size.

Another type of spider, found in Thailand and of interest because it attacks a species of mosquito known to carry the virus that causes Dengue fever, is less of a wrestler and more of a cowboy. It captures mosquitoes by lassoing them with a strand of silk that it throws with its hind legs.

Spiders around the world eat mosquitoes. Spiders do not have to be cowboys or wrestlers to nab mosquitoes, though. They can also catch them the old-fashioned way, because mosquitoes do get caught in webs.